1. Field of the Invention
This invention relates to an antenna for use in detecting electromagnetic noise radiation in which a high frequency, asymmetric signal was generated. More specifically, this invention relates to a loop antenna design which uses two loops that are run in opposite direction to each other, thereby resulting in two out-of-phase signals being detected in the loops which are then combined as the antenna output.
2. Description of Related Art
Electromagnetic noise radiation can result from a variety of sources, for example, electrical arcs or sparking gaps. Such signals can cause radio interference or noise. More importantly, such signals result from an electrostatic discharge (ESD) which are incapable of even being perceived by a human being but which can cause significant damage to sophisticated electronic equipment.
It is well known in the art that a loop antenna system is particularly useful in sensing radiate fields from electrical arcs. An example of such a system is disclosed in U.S. Pat. No. 4,214,210, issued to Martin O'Shea on Jul. 22, 1980 and entitled "Electromagnetic Noise Source Locator". One advantage of such a loop antenna system is its ability to sense a broad frequency spectrum. However, it is also well known that the sensitivity of a loop antenna is affected by its orientation to the signal source. Such a characteristic may be of use in locating the direction of the source of a continuous signal. However this sensitivity is a significant disadvantage in measuring or even recognizing a single electric arc occurring at a location whose direction is unknown.
An additional consideration in ESD event detectors is exemplified in U.S. Pat. No. 4,631,473 issued to Masamitsu Honda on Dec. 23, 1986 and entitled "Transient Electromagnetic Field Detector". This Honda patent relates to providing a momentary indication of the existence of an ESD event by comparing the amplitude of a received signal's waveform against a predetermined threshold, irrespective of how may ESD events the received signal waveform actually represents. That is, a single ESD event produces electromagnetic radiation which may be reflected by nearby metallic objects, resulting in the receipt of several signal peaks above a predetermined threshold. Thus, a significant limitation on the accuracy of existing ESD detectors is their ability to distinguish a multi-peak waveform representing a single ESD event from a waveform that represents several ESD events. Such accuracy is critical in determining the relative effectiveness of various proposed methods of ESD mitigation in environments where electronic devices prone to ESD damage, are assembled and used.
Applicants' copending U.S. patent application Ser. No. 08/842,920 filed Apr. 17, 1997 and titled "Electrostatic Discharge Event Detector" (and subsequently allowed Nov. 23, 1998), hereby incorporated by reference, relates to a device which is able to distinguish multi-peak waveforms resulting from a single ESD event. To make such a distinction, this device or alternative devices performing the same function must evaluate signals whose frequency readily exceeds 1 GHz (10.sup.9 Hz). That is, any device, which receives as input the ESD wave signal detected by a conventional antenna, must be capable of processing this signal at this high frequency rate to be able to properly evaluate if a single ESD event has occurred.